Thanks, found another manual online this shows more clearly that the bottom fixing does not go through the supplied supporting plate but is bored through the back of the awning min 60 mm from end, whereas the supplied supporting plate is 300 mm from end.
Presume its done at each end as the fittings are provided to allow that: 4 single backing plates: two for the middle supporting plates and 2 for these end fixings
The internal shelving in the van is in the way which explains why it was not done for the original install.